The present invention pertains to the separation and recovery of electrophotographic toner compositions, particularly concentrates, to effectively and efficiently isolate the pigment and associated charged body material therein for reclamation and re-use (or other desired disposition on an individual basis(;) and the objects and aims of the invention are to provide an advantageous and beneficial treatment and technique for accomplishment of the indicated purpose(s).
Change-responsive dye or pigment colorants (which includes black), generally called "toners", are well known in the electrophotographic art for developing and fixing in black-and-white or plural color reproductions the latent images imposed by activating influences, such as light, on sensitized and exposed image-retaining electrophotographic base materials. The electrophotographic phenomenon for both the so-called line copy and actual pictorial reproduction is well known in the art. Amongst the copious patent and literature material available thereon, reference may be had to U.S. Pat. Nos. 3,052,539; 3,249,430; 3,259,581; 3,383,209; 3,595,691; 3,660,086; 3,751,247; 3,758,305; 3,802,880; and 3,809,555 and the numerous citations therein amongst the multitudinous additional teachings and disclosures available in the art (such as those included, inter alia, in International Search Classes G03f, G03g and so forth). A good standard reference in the electrophotographic field is "Xerography And Related Processes" by Dessauer and Clark, 1965 Edition, published by Focal Press. Various electrophotographic base materials and colorants, as well as other more specialized teachings and disclosures, may in addition to the above be discerned in U.S. Pat. Nos. 2,891,911; 3,078,231; 3,249,430; 3,259,581; 3,296,140; 3,639,243; 3,639,244; 3,802,880; 3,804,619; and 3,809,555 plus Canadian Pat. Nos. 846,740; 846,741 and 846,742. Thus, no further fundamental elucidation or detailed description is necessary or required as to same for full comprehension and clear understanding of the present invention.
In general, toner colorants are pigments or dyestuffs (or combinations thereof) that are coated with usually a plastic or resinous binder and dispersed in a suitable mineral spirit or normally liquid hydrocarbon material from petroleum or the like with (although other additives of a charge-responsive nature or having other desired characteristics may also be present) a very minor proportion -- almost in trace quantities on the order of 1 - 1,000 ppm by wt. and more often between about 10 and 50 ppm -- of charge control or directing agents which tend to direct and accurately control good deposition and lay-down of the colorant during latent image development and fixing.
As with the pigments or dyestuffs and resin binders therefor, many of a wide variety of suitable charge control agents are suitable for use in toner compositions. Typical of these are cobalt naphthanate, manganese octosol, (scientifically boiled) linseed oil, asphaltum, ollyl acid phosphate and the like and equivalent materials. As is above indicated, the toners generally employ only literal trace amounts of the charge control agent(s), with maximum ranges involved for at least rough comparison with those above specified in ppm being, on a wt. % based on total solids in the toner, between about 0.1 or 0.15 to 0.3 or 0.4%.
Many of a wide variety of organic and inorganic pigments and/or dyestuffs may be utilised as the colorant in the toner including such materials as various carbon blacks; asphaltums; specific and oftentimes proprietary materials such as the colorants "Phthalocyanine Blue", "Rhodamine B", "Benzidine Yellow" and so forth; various oxides, sulfates, sulfides, carbonates, phosphides, phosphates, nitrates, nitrites and the like of alkali metals, alkaline earth metals, a large number of the heavy metals and, frequently, organic derivatives of the straightforward inorganic pigment colorants; and so forth. Likewise, in order to obtain satisfactory coated pigment and/or dyestuff materials for toner colorant usage, many of wide variety of usually resinous or plastic (most often thermoplastic and fusible) binder materials can be employed including, for purposes of illustration, various vinyl resins, regular and modified arcylic resin polymers, methacrylates (including the methyl, methyl/n-butyl, ethyl, butyl, etc., varieties), regular and modified alkyd resin types, vinyl acetate polymers, vinyl butyral polymers, and so forth. Usually, the pigment to binder ratio in a toner colorant is such that there is between about 2 and about 10, more commonly 6 - 8, parts by weight of binder(s) to each part by weight of the pigment or dyestuff in the composition (with mixed pigment and/or dyestuff as well as mixed resin binder systems being possible to utilize); with the total solids dispersed in the vehicle ordinarily, on a % by wt. basis, no more than in the range of 0.2 to 1.5% taken on total toner composition with solids in the range between about 0.3 and about 1.1% by wt. being more typical.
Of course and as has been indicated, toner concentrates treated and in practice are those toner compositions which are prepared wherein the resin coated colorant with other additives combined is made up for subsequent dispersion in the desired solvent at the appropriate desired concentration for toner usage.
A predominantly aliphatic type normally liquid hydrocarbon mineral spirit or oleaginous material is frequently employed as the solvent or vehicle in the toner concentrate composition. An especially desirable solvent for the toner concentrates is an inert, highly dielectric, paraffinic oleaginous material (generally derived from petroleum stocks although synthesized equivalents may be utilized) of the type frequently employed as a transformer oil which has viscosity and gravity characteristics at least approximately, if not generally, in the range of those exhibited by motor oils for internal combustion and other engines between about 10W and 40W according to S.A.E. standards. Toner concentrates are capable of being prepared and handled with an advantageous economy of bulk or volume, and generally have desirably long storage and shelf-life properties, until actual preparation therefrom of the toner to be utilized therefrom.
When toner concentrates are dispersed (or diluted) to provide actual practical toner compositions, a wide variety of solvents may be utilized for the purpose. Good illustrations of these are the paraffin and isoparaffin types and varieties, such as those in the approximate C.sub.16 range and which are known and avaiable under such trade designations are "Isopar G"; "Isopar H"; "Shell Sol 70"; and "Shell Sol 71", although sometimes solvents with such constituents as the aromatic mineral spirits may be employed, including such commercially available material as "Solvesso 100". It is ordinarily desirable for the mineral spirit solvent employed for dilution of the toner concentrate, however, to contain not more than about 10 wt. %, preferably less than 5% by wt., of aromatic constituent in the toner composition and for it to have a solubility parameter range according to the well-known and conventional concept on the numerical order between about 4 to 15, especially in the more narrow area between about 6 and 10.
On development and fixing of latent images in electrophotographic processes, toner compositions usually are considered to become more or less ineffective and spent or depleted when about 1/2 or so of the original solids content (as may be provided from a concentrate utilized for the toner preparation) is deposted out of the composition as a colorant for the electrophotographic copy reproduction(s) being made; this consideration being of course applicable to liquid toner systems. In the case of pictorial (rather than line copy) reproductions, this can happen as quickly as the 5th or so print of approximate maximum 5 inches .times. 7 inches reproduction using a toner bath volume of about 1,000 cc's. with a solids concentration in a given toner on the order of 0.7 wt. % of involved composition.
While concentrate may be added to a depleted toner in order to reconstitute or recondition and refresh it to its original position of colorant depositing capacity, this is not always desirable or easy to perform since in the process of toner depletion there tends to be a non-uniform utilization of toner ingredients (besides the colorant pigment and/or dyestuff) and proper adjustment without resort to or indulgence in possibly difficult analytical control techniques may be difficult in order to avoid undesirable imbalances of constituents, particularly charge control agent which can leach out the resin binder when present in too large or too small proportions, so as to preclude optimum operability and performance of the toner. Thus, excess quantities prepared in advance of toner concentrate greater than those actually required for toner preparation are not always utilizable or consumable in any desirable or practical way and, oftentimes with great advantage, are recovered according to the present invention.
Furthermore, toners are generally difficult to separate into original components especially on an economical and practically useful and attractive basis. Hence, the usual practice with toner composition concentrates incapable of practical utilization is to simply discard them as waste, since (because of their particular composition) they tend to have very limited, if any, diverse applicability and utility despite the fact that their original components can be employed for many things.